Numerous environmental and endogenous chemicals can initiate cancer. A slight change in structure may distinguish carcinogenic chemicals from harmless ones. The relation between chemical structure and cancer-causing potential will be investigated for polycyclic aromatic hydrocarbons (PAHs), a representative class of chemical carcinogens. On metabolic activation, PAHs react with DNA, causing mutations in tumor suppressors and oncogenes, which initiate cancer. This proposal focuses on human nucleotide excision repair (NER) of PAH-damaged DNA and the effect of PAH-modified templates on the replication process within polymerases. The overall hypotheses are: (i) The specific conformation of damaged DNA determines whether it is repaired, (ii) If repair fails, the DNA conformation within a polymerase determines whether blockage, normal, or mutagenic bypass occurs. It is hypothesized that differences in local polymerase structure, adduct topology, adduct stereochemistry, and local base sequence context govern the lesion treatment in NER and translesion synthesis. The method of determining structure employs molecular modeling to delineate structural, dynamic, and thermodynamic properties of DNA adducts. In Specific Aim 1, variation of detailed structure with sequence for guanine and adenine adducts derived from the bay region PAH, benzo[a]pyrene and the fjord region PAHs benzo[c]phenanthrene and dibenzo[a,l]pyrene will be determined, in order to delineate structural and thermodynamic features governing NER. In Specific Aim 2, we propose to delineate structural alterations in polymerase-primer-template-dNTP ternary complexes caused by a PAH adduct at the template. The focus is on error-prone lesion bypass polymerases, and replicative polymerases, to determine structural features leading to blockage, mutagenic bypass, or error free translesion synthesis. The long term goals are to define conformational details governing NER and translesion DNA synthesis to gain predictive power relating lesion structure with carcinogenic hazard.